For last christmas my cousin gifted me an EVGA gtx 570 HD, I bought all the components he told me I needed for it and took it to someone to set it up for me, I was reading and it's supposed to run pretty well for most games I would like to play, however for all of the games I've tested it on, it's a bare minimum improvement from what I used to play on, as an example I play Team Fortress 2 a lot which is a pretty old game at this point it should run well in most PCs, but even on lowest settings and borderless windowed, FPS stays at 57 max and has hit as low as 26 fps, even on older games, sometimes my display just turns black out of nowhere and the fans on the GPU stop spinning as if the gpu reset.
I installed the latest drivers, I've ran the benchmark test multiple times and says everything is fine, the test even reaches 140+ fps stable, I checked and changed the cables, nothing seems to fix it.
 
Specs:
OS: Windows 8.1 Pro 64bit
System Manufacturer: Gigabyte Technology
Processor: AMD A4-4000 APU Radeon HD Graphics (2CPUs 3.0ghz)
Memory: 4096MB RAM
Direct X: DX 11
Power Source: EVGA 500W 80+ Certified Power Supply
MotherBoard: Gigabyte F2A68HM-DS2H Ultra Durable Socket FM2+
 
Any help will be greatly appreciated, thanks in advance.

GPU temp varies from game to game, between 34 - 66
GPU clock varies between 50 to 797 depending on the games I've tested
Memory Clock varies between 135 and 1951 depending on the game as well
 
I only have 1 monitor so I wouldn't know but the times it's done it, my monitor never said "no signal" or anything like it

I've only tried with the latest drivers, I'll download older ones and check.
The black screen issue has happened with almost every game I've tested so far.
 
Edit: I just got done testing 4 different drivers, nothing changed with any of them.

Ok, I'll see if I can test it on another PC then.
Thanks for your help!